Brushless DC (direct current) electric motor (BLDC motors, BL motors) also known as electronically commutated motors (ECMs, EC motors) are synchronous motors that are powered by a DC electric source via an integrated inverter/switching power supply, which produces an AC (alternating current) electric signal to drive the motor. In this context, AC does not imply only a sinusoidal waveform, but rather a bi-directional current with no restriction on waveform. Additional sensors and electronics may control the inverter output amplitude and waveform in order to control DC bus usage/efficiency and frequency (i.e. rotor speed).
Digital motor control was first introduced to overcome the challenges that traditional analog systems had in handling drift, aging of components and variations caused by temperature. Flexible software algorithms not only eliminated tolerance issues relating to components, they enabled developers to dynamically accommodate variations in environmental conditions over time. For example, rather than only being able to turn a fan motor full on or off, fan speed can now be adjusted based on system temperature with a digital implementation. Additionally, systems may calibrate themselves, thus eliminating the need to schedule regular, manual maintenance.
Hall sensors are the industry choice for medium sensitivity magnetic sensors due to low cost, small area, and easy integrability. However, semiconductor Hall sensors may suffer from offset resulting from nonidealities such as mismatch, doping variations, and undesired piezoelectric effects. A technique referred to as “spinning current” may be used to reduce the offset.
The so called “Hall Effect” occurs when a magnetic field is oriented perpendicular to an electric current. The magnetic field generates a voltage difference across a conductor, called the Hall Voltage, in a direction which is perpendicular to both the direction of the magnetic field and the direction of the current flow. By measuring the Hall voltage it is possible to determine the magnitude of the magnetic field. Typical Hall sensors usually include a strip or plate of an electrically conductive material with an electric current flowing through the plate. When the plate is positioned in a magnetic field such that a component of the field is perpendicular to the plate, a Hall voltage is generated within the plate in a direction that is perpendicular to both the direction of the magnetic field and the direction of the current flow.
Semiconductor Hall effect sensors produced using current techniques typically include a sensing element produced from silicon. The magnetic sensitivity of these devices is directly related to the electron mobility, mu, of the material used to construct the sensing element. Silicon typically has an electron mobility of approximately 1500 cm2/(Vs).
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.